This section is intended to provide a background to the various embodiments of the invention that are described in this disclosure. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and/or claims of this disclosure and is not admitted to be prior art by the mere inclusion in this section.
Universal Mobile Telecommunications System (UMTS) is the 3rd Generation (3G) mobile communication system standardized by 3rd Generation Partnership Project (3GPP). The 3GPP launched a study item known as “Long Term Evolution (LTE)”. The study will investigate means of achieving major leaps in performance in order to improve service provisioning, and to reduce user and operator costs. Out of that and because interworking with other radio access technologies should be possible, the need arose for a new evolved Packet Core Network.
In general, in such mobile communication systems, a terminal device (also called User Equipment (UE)) has access to communication services (including basic services such as in particular providing IP connectivity) via a network comprising a Core Network (CN) accessed by an Access Network (AN).
An example of 3GPP-based mobile communication system is Evolved Packet System (EPS), a description of which can be found in particular in 3GPP standards such as for example 3GPP TS 23.401 and 3GPP TS 23.402 series.
According to the 3GPP standards, EPS includes Evolved Packet Core (EPC) that can be accessed by various access networks, including 3GPP based access networks and non-3GPP based access networks. Examples of 3GPP based access networks include UMTS Terrestrial Radio Access Network (UTRAN), evolved UTRAN (E-UTRAN), GSM EDGE Radio Access Network (GERAN), etc. Examples of non-3GPP based access networks include CDMA2000, Wireless Fidelity (WiFi) Access Network (specified by IEEE, in particular in 802.11 specifications), Worldwide Interoperability for Microwave Access (WiMAX) Access Network (specified by IEEE, in particular in 802.16 specifications).
Two different types of non-3GPP based access networks are involved in the 3GPP standards, i.e. untrusted non-3GPP based access networks and trusted non-3GPP based access network, and normally whether a non-3GPP based access network is trusted or not is left to specific 3GPP operators. During initial attach or handover attach a UE needs to discover the trust relationship (whether it is a trusted or untrusted non-3GPP access network) of the non-3GPP access network in order to know which non-3GPP IP access procedure to initiate.
Some calling solutions enable mobile subscribers to make voice calls (initially) from an untrusted non-3GPP based access environment, such as from residential WiFi. The calls are managed by IP Multimedia Subsystem (IMS) Core, and the solution is sometimes referred to as Voice over Wi-Fi. Those solutions also enable the user to maintain session continuity or IP address persistency when they handover between 3GPP based access (such as for example LTE) to untrusted non-3GPP based access (such as for example WiFi).
The procedures of non-3GPP Packet Date Network (PDN) connection establishment over untrusted non-3GPP access and the handover between 3GPP based accesses and untrusted non-3GPP accesses are defined in 3GPP TS 23.402 and TS 23.401 series.
However, as to the emergency call service, the current 3GPP standards do not support emergency calls over an untrusted non-3GPP accesses (e.g., WiFi) and emergency session continuity for the handover between a 3GPP based access network and an untrusted non-3GPP based access network. Specifically, in the current 3GPP standard: IMS Emergency Session setup over untrusted non-3GPP based access (e.g., WiFi) is not supported; IMS Emergency Session Support for non-3GPP accesses connected to EPC is limited to support of handover of emergency sessions from E-UTRAN access to High Rate Packet Date (HRPD) access (which is normally configured as a trusted access by operators); handover of IMS Emergency Sessions from non-3GPP access to 3GPP based access (e.g., E-UTRAN) is not supported.